The present invention relates to a novel curable epoxy resin composition or, more particularly, to a curable epoxy resin composition suitable for use in the resin encapsulation of various electric or electronic parts.
As is well known, many of electric parts and electronic devices are used as encapsulated with a synthetic resin. Curable epoxy resins belong to one of the most important classes of the resins for such an application including encapsulation of not only transistors and diodes but also more delicate electronic devices such as ICs and LSIs by virtue of the excellent properties of the cured epoxy resins as well as the good moldability thereof in shaping by the techniques of transfer molding, injection molding and the like.
These epoxy resin compositions, however, still have several problems desirably to be solved. They are, for example, as follows.
(1) The electric or electronic parts encapsulated with a cured resin composition are unavoidably under the influence of the stress produced in the resin composition by the curing thereof leading to eventual distortion or, in sometimes, breaking of the parts. In particular, this problem is more serious in the ICs and LSIs of recent years becoming larger and larger in size with increasing degree of integration so that they are frequently fractured as a consequence of the excessively increased strain.
(2) Attempts have been made to decrease the stress in the cured epoxy resin composition by formulating the resin composition with a different kind of a resin having larger flexibility or with a fribrous material or increasing or by increasing the amount of the inorganic filler. These methods are not without their own respective drawbacks despite the decrease of the stress caused by curing of the resin. For example, formulation of a flexible resin results in decreased anti-moisture resistance of the resin encapsulation along with a lowered glass transition temperature of the resin. Formulation of a fibrous material is undesirable due to the remarkably increased bending of the very fine wires of gold, aluminum and the like used for wiring between the chip and the outer lead wires resulting in frequent wire breaking. Further, a resin composition formulated with an increased amount of an inorganic filler has poor flowing characteristics so that difficulties are encountered in the encapsulation with the resin composition by transfer molding, injection molding and the like molding method so that the stress in the cured resin composition is not decreased as desired.
Accordingly, there has long been desired to develop a novel and improved curable epoxy resin composition which can satisfy the requirement of low stress after curing in the resin encapsulation of ICs and LSIs of large size and with high degree of integration and can be free from the lowering of the glass transition temperature and decrease in the anti-moisture resistance of the resin-encapsulated electronic devices.